Amplifiers are used in a wide variety of integrated circuits (IC's). One particular application is in a power or boost converter, where a regulated voltage such as an internal power-supply line has its voltage fed back to an error amplifier. The error amplifier compares the regulated voltage to a reference voltage. The difference or error is amplified and used to control a power transistor that adjusts the regulated voltage. The error is driven toward zero by a feedback loop.
Of course, error amplifiers may be used in other applications, such as in Analog-to-Digital Converters (ADC), boost circuits, voltage comparators, etc. While the exact design requirements for error amplifiers may vary, oftentimes an error amplifier that is stable yet has a fast response time is desirable.
Slew rates can be enhanced by increasing bias currents. However, increased bias currents can have unintended effects in error amplifiers.
Error amplifiers often use differential transistors. However, when bias currents are increased, shutting off one differential transistor or a circuit leg containing the differential transistor may be difficult. Adaptive biasing may lower the source voltages of differential transistors, causing both differential transistors to remain on. Without the extra bias current, one differential would turn off as desired.
Positive feedback may also cause stability issues in an error amplifier. Multiple stages may be used, but the extra stages complicate the circuit and increase die area and costs. Multiple dominant poles may result, creating further stability issues. Controlling the threshold for the slew rate enhancement may also be challenging. A single pole amplifier is more desirable.
A high slew rate amplifier is desired that is still stable. An error amplifier with dominant pole compensation is desirable, especially for switching power converter applications and in other high-speed systems.